1）编写待编译的java类

package f_asm_and_javassist;

import jdk.internal.org.objectweb.asm.*;

import java.io.*;

import static jdk.internal.org.objectweb.asm.Opcodes.ASM5;

/**

* @Author zhangboqing

* @Date 2020/3/26

*/

public class AsmDemo {

//访问类的方法和字段

public static void main(String[] args) {

byte[] bytes = getBytes(); // MyMain.class 文件的字节数组

ClassReader cr = new ClassReader(bytes);

ClassWriter cw = new ClassWriter(0);

ClassVisitor cv = new ClassVisitor(ASM5, cw) {

@Override

public FieldVisitor visitField(int access, String name, String desc, String signature, Object value) {

System.out.println("field: " + name);

return super.visitField(access, name, desc, signature, value);

}